We know dyes color our food, clothes, and other everyday items, but do we know how they work? The process of dying has been crafted and manipulated since ancient discoveries of natural pigments in plants, roots, and insects. The process of dyeing has existed since its beginnings in India more than 5000 years ago.1 Unlike the dyes that are used for mass-production today, ancient dyes were all natural and required intricate and meticulous extraction methods which are still mirrored by modern machines today. Generally, dyes can be categorized based on the process it takes to make them: Organic dyes are human-made, synthetic dyes that have a finite and specific chemical composition. Synthetic dyes are less costly and easier to make, quickly replacing the previous type of dyes, natural dyes. Natural dyes are purely animal, vegetable or mineral-based and, although effective, can be mimicked by organic dyes because they are often more rare and thus more expensive to manufacture. Food dyes are unique in that they utilize both natural and chemical dyes regularly, but are about the only modern industry to do so.
When comparing and contrasting dyes, there are some basics that make one dye different from another. There are many factors that can differentiate dyes, such as: color fastness, a measure of how well a dye is attached to its substrate (normally a fabric), permanence, a measure of how long the bond between the substrate and dye normally lasts, and the use of the dye, whether for food, textiles, pharmaceuticals or medical.
In order to fully understand the way dyes work, we need to understand the beginnings of the dye industry, and how it’s developed form that point on. The first synthetic dye ever made was discovered accidentally by William Henry Perkin in 1856. Originally trying to create a cure for malaria by synthesizing a rare natural extract, he stumbled upon a crude aniline mixture that when extracted with alcohol turned a bright purple color. Perkin used an aniline mixture, which is colorless on its own, but can create anywhere from a rusty brown when oxidized, to a deep black when added to certain metallic salts. Aniline is one of the simplest kinds of amines, and is a combination of a phenyl group attached to an amino group, and is formed from benzene. Perkin used his newly acquired knowledge of anilines to perfect the dye he later called mauveine. Prior to his discovery, the only dye used to create a purple hue was Tyrian Purple, a totally natural dye first produced by the ancient Phoenicians. Tyrian purple was incredibly expensive, because of its general use as a exclusively royal dye. The dye was prized by Romans as a symbol of wealth and, because of its richness of color, was considered a luxury meant only for those who could afford it. Mauveine’s entrance into the market was welcomed for just this reason: it could be synthesized commercially and in large batches. Whereas originally a purple hue could only be achieved by the painstaking process of the decomposition of varied types of snails (as was customary for the production of Tyrian Purple), the simple chemical composition of mauveine made it a hit on the market and gave it an important role in the Industrial Revolution. 2
Along with Tyrian Purple, many natural dyes made the creation of synthetic dyes possible. Important dyes such as indigo were economically vital, as the color blue was once hard to find and harder to make. Made from the extraction of a substance called indican from certain leaves, indigo was revolutionary in its extraction method as well as the colors it yielded. In order to make indigo, the leaves were soaked in water and fermented, to create dried leaf-cakes, which could produce the blue colored powder dye when combined with a strong base such as lye. This process could be easily duplicated in a lab, which is why unlike Tyrian purple, indigo can be synthesized and most indigo today is man-made. Interestingly, the development of natural dyes and even the beginning of the synthesis of some of these dyes began before scientists really knew how color dyeing worked. At the tail end of the Industrial Revolution many scientists attempted to gain a basic understanding of dyeing as it related to their current knowledge of how color worked. Basically, they only knew the hue of the dye was determined by the wavelength it absorbed, and a change in the respective structures of dyes gave the dyes unique hues. A shift in the structure that causes the absorbtion of longer wavelengths is called a bathochromic shift, and the reverse, towards shorter wavelengths, is called a hypsochromic shift 3.
From basic knowledge and a perception of the rich opportunities in the growing field of textiles and dyeing, many scientists scrambled to explain the construction and reaction of dye molecules. In 1876, a German scientist, Otto N. Witt, proposed his theory of chromophores and auxochromes: that dye molecules contain both chromophores and auxochromes, which are grouped together by a conjugated system, which joins two covalently bonded atoms, and determine the color of the dye. He discovered that the chromophore is usually electron-withdrawing, and the auxochrome is electron-donating. From this basis, Witt determined that bathochromic shift, or a shift towards a longer wavelength and the violet- blue- green- side of the color wheel, could be achieved by increasing the withdrawing power of the chromophore, and thus the donating power of the auxochrome. When this shift occurred, it was found that the conjugated system connecting the two was also lengthened. It was later found that the positions of the auxochrome and chromophore groups were important as well, generally the Meta position made for shorter wavelengths than approximately equal wavelengths created by the Para and Ortho positions. This theory helped explain the reasons for the different colors created by indigo and Tyrian Purple’s chemical compositions 4,5:
Tyrian Purple
Indigo
Not only did Witt’s discovery allow for an increased understanding of natural dyes, but it fostered a dramatic spike in the production of synthetic dyes. Some dyes are man-made to mimic the colors created in nature by natural pigments, and those dyes are called synthetic. There are many advantages to these dyes, but a main one is that they can be engineered to be attached to substrates that cannot be accessed by natural dyes, such as polyester, nylon and other artificial textiles. Disperse Dyes are used to dye fabrics such as these, and have a unique ability to sink into tightly-packed polymer chains, whereas other dye molecules are too large and rigid to do so. Normally planar, non-ionic, and made up of small carbon chains with attached functional groups like NO2- and CN-, disperse dyes have the important ability to dye normally stubborn and repellant fabrics. Since polymers have a more crystalline structure than say, a linen, high temperatures and pressures are necessary to soften the polymers tight bonds and create more openings for the dye to enter. Because of the more specialized processes used to dye polymers and other synthetic fabrics, synthetic dyes were a huge factor in creating efficiency for mass-production and commercialization of dyes.
Today, you can’t look anywhere without encountering a variation on one of these dyes. They color the world, and the simple manipulation of auxochromes and chromophores allow for brilliant colors to be created everyday. The dye industry has expanded and is now used widely in the pharmaceutical and medical fields, the beauty industry, and obviously, textile dyeing. Without dyes, the world would be colorless and bland, and oftentimes in order to appreciate the presence of color in your life, all you have to thank is a dye.
Procedure
First, I made the alum mordant by simmering a 500 ml of water in a 1000 ml beaker. While the water is heating, I weighed my yarn, which ended up being 9.18 grams. Then i measured out .918 grams of potassium aluminum sulfate (10% of the weight of the yarn) and .459 grams of cream of tartar (5% of the weight of the yarn). Once the water heated to just under boiling, about 90 degrees, I added the potassium aluminum sulfate and the tartaric acid to the beaker. Once the mixture was completely dissolved, i dampened the yarn by running it under some clean water and put the yarn in the beaker. Keeping the mixture at about 90 degrees consistently, I simmered the mixture for an hour, stirring occasionally to ensure that the yarn was fully submerged. After an hour of simmering, I removed the yarn and spread it out on a paper towel to dry completely before I dyed it.
In order to dye both the untreated yarn, which weighed 9.32 grams, and the Alum mordant-treated yarn, which weighed 9.18 grams, I used the same procedure for both, in separate batches: First I measured out exactly 1 oz. of dry, whole cochineal. I then used a mortar and pestle to grind the dry cochineal into a fine and uniform powder. Then I placed the cochineal powder into a 250 ml beaker and covered with 200 ml water, which I stirred to ensure that the powder was fully dissolved. I then let the cochineal mixture sit overnight to increase its depth of color. I repeated this process to make 2 identical dyes- 1 for the alum-mordant-treated yarn and 1 for the untreated yarn. The next day, I filled a 1000 ml beaker with 500 ml water and brought it to a boil. I then added the cochineal mixture and brought it back up to a boil, boiling for 15 minutes. During this 15 minutes, I made sure to skim off the froth and the impurities and solids that were rising to the top of the mixture, and discarded these. I then dampened the untreated yarn and added it to the mixture, mixing occasionally and simmering for 45 minutes at 95 degrees. I repeated this same procedure for the alum-mordant-treated yarn. After 45 minutes, I removed both the yarn skeins and spread them on paper towels to dry. After letting them dry for about an hour, I washed them in a cold-water bath to seal the color in, and spread them out again to dry fully.
Results
The results of my experiment surprised me in a couple different ways. Firstly, I was surprised by the dramatic difference in the colors produced by the same dye when one yarn was treated and one yarn wasn't: The alum-treated yarn created a much deeper scarlet color, while the untreated yarn produced a much more pink-purple color. Secondly, I was also surprised by how well the dye held to it's substrate: After washing both the yarns in cold-water baths, the colors have not leaked into the water at all, becoming more and more intact the more they were able to dry. Overall, I was satisfied with the results in both the quality of the dye and the noticeable difference in the colors the two treatments produced.
Conclusions
When using a homemade dye, a difference in color and depth of color can be produced by treating the yarn beforehand, in this case with an alum mordant.
In my experiment, the results were good but could have been improved in several ways. First, I think that straining the cochineal mixture after letting it sit overnight would have eliminated the need to skim off solids from the dye-bath when it was boiling and would have produced a cleaner experiment. There are also several other treatments that you can use to create different colors and depths of color, including after-treatments which are applied after the dyeing itself, which would have been interesting to experiment with. A lot of my experiment was done at home, which made some of the measurements more difficult to obtain, and so the accuracy of the liquid measurements I also feel could have been improved by doing the entire experiment in the lab.
Table of Contents
Chemistry of Dyes
Ella RadcliffeIntroduction
We know dyes color our food, clothes, and other everyday items, but do we know how they work? The process of dying has been crafted and manipulated since ancient discoveries of natural pigments in plants, roots, and insects. The process of dyeing has existed since its beginnings in India more than 5000 years ago.1 Unlike the dyes that are used for mass-production today, ancient dyes were all natural and required intricate and meticulous extraction methods which are still mirrored by modern machines today. Generally, dyes can be categorized based on the process it takes to make them: Organic dyes are human-made, synthetic dyes that have a finite and specific chemical composition. Synthetic dyes are less costly and easier to make, quickly replacing the previous type of dyes, natural dyes. Natural dyes are purely animal, vegetable or mineral-based and, although effective, can be mimicked by organic dyes because they are often more rare and thus more expensive to manufacture. Food dyes are unique in that they utilize both natural and chemical dyes regularly, but are about the only modern industry to do so.
When comparing and contrasting dyes, there are some basics that make one dye different from another. There are many factors that can differentiate dyes, such as: color fastness, a measure of how well a dye is attached to its substrate (normally a fabric), permanence, a measure of how long the bond between the substrate and dye normally lasts, and the use of the dye, whether for food, textiles, pharmaceuticals or medical.
In order to fully understand the way dyes work, we need to understand the beginnings of the dye industry, and how it’s developed form that point on. The first synthetic dye ever made was discovered accidentally by William Henry Perkin in 1856. Originally trying to create a cure for malaria by synthesizing a rare natural extract, he stumbled upon a crude aniline mixture that when extracted with alcohol turned a bright purple color. Perkin used an aniline mixture, which is colorless on its own, but can create anywhere from a rusty brown when oxidized, to a deep black when added to certain metallic salts. Aniline is one of the simplest kinds of amines, and is a combination of a phenyl group attached to an amino group, and is formed from benzene. Perkin used his newly acquired knowledge of anilines to perfect the dye he later called mauveine. Prior to his discovery, the only dye used to create a purple hue was Tyrian Purple, a totally natural dye first produced by the ancient Phoenicians. Tyrian purple was incredibly expensive, because of its general use as a exclusively royal dye. The dye was prized by Romans as a symbol of wealth and, because of its richness of color, was considered a luxury meant only for those who could afford it. Mauveine’s entrance into the market was welcomed for just this reason: it could be synthesized commercially and in large batches. Whereas originally a purple hue could only be achieved by the painstaking process of the decomposition of varied types of snails (as was customary for the production of Tyrian Purple), the simple chemical composition of mauveine made it a hit on the market and gave it an important role in the Industrial Revolution. 2
Along with Tyrian Purple, many natural dyes made the creation of synthetic dyes possible. Important dyes such as indigo were economically vital, as the color blue was once hard to find and harder to make. Made from the extraction of a substance called indican from certain leaves, indigo was revolutionary in its extraction method as well as the colors it yielded. In order to make indigo, the leaves were soaked in water and fermented, to create dried leaf-cakes, which could produce the blue colored powder dye when combined with a strong base such as lye. This process could be easily duplicated in a lab, which is why unlike Tyrian purple, indigo can be synthesized and most indigo today is man-made. Interestingly, the development of natural dyes and even the beginning of the synthesis of some of these dyes began before scientists really knew how color dyeing worked. At the tail end of the Industrial Revolution many scientists attempted to gain a basic understanding of dyeing as it related to their current knowledge of how color worked. Basically, they only knew the hue of the dye was determined by the wavelength it absorbed, and a change in the respective structures of dyes gave the dyes unique hues. A shift in the structure that causes the absorbtion of longer wavelengths is called a bathochromic shift, and the reverse, towards shorter wavelengths, is called a hypsochromic shift 3.
From basic knowledge and a perception of the rich opportunities in the growing field of textiles and dyeing, many scientists scrambled to explain the construction and reaction of dye molecules. In 1876, a German scientist, Otto N. Witt, proposed his theory of chromophores and auxochromes: that dye molecules contain both chromophores and auxochromes, which are grouped together by a conjugated system, which joins two covalently bonded atoms, and determine the color of the dye. He discovered that the chromophore is usually electron-withdrawing, and the auxochrome is electron-donating. From this basis, Witt determined that bathochromic shift, or a shift towards a longer wavelength and the violet- blue- green- side of the color wheel, could be achieved by increasing the withdrawing power of the chromophore, and thus the donating power of the auxochrome. When this shift occurred, it was found that the conjugated system connecting the two was also lengthened. It was later found that the positions of the auxochrome and chromophore groups were important as well, generally the Meta position made for shorter wavelengths than approximately equal wavelengths created by the Para and Ortho positions. This theory helped explain the reasons for the different colors created by indigo and Tyrian Purple’s chemical compositions 4,5:
Tyrian Purple
Indigo
Not only did Witt’s discovery allow for an increased understanding of natural dyes, but it fostered a dramatic spike in the production of synthetic dyes. Some dyes are man-made to mimic the colors created in nature by natural pigments, and those dyes are called synthetic. There are many advantages to these dyes, but a main one is that they can be engineered to be attached to substrates that cannot be accessed by natural dyes, such as polyester, nylon and other artificial textiles. Disperse Dyes are used to dye fabrics such as these, and have a unique ability to sink into tightly-packed polymer chains, whereas other dye molecules are too large and rigid to do so. Normally planar, non-ionic, and made up of small carbon chains with attached functional groups like NO2- and CN-, disperse dyes have the important ability to dye normally stubborn and repellant fabrics. Since polymers have a more crystalline structure than say, a linen, high temperatures and pressures are necessary to soften the polymers tight bonds and create more openings for the dye to enter. Because of the more specialized processes used to dye polymers and other synthetic fabrics, synthetic dyes were a huge factor in creating efficiency for mass-production and commercialization of dyes.
Today, you can’t look anywhere without encountering a variation on one of these dyes. They color the world, and the simple manipulation of auxochromes and chromophores allow for brilliant colors to be created everyday. The dye industry has expanded and is now used widely in the pharmaceutical and medical fields, the beauty industry, and obviously, textile dyeing. Without dyes, the world would be colorless and bland, and oftentimes in order to appreciate the presence of color in your life, all you have to thank is a dye.
Procedure
First, I made the alum mordant by simmering a 500 ml of water in a 1000 ml beaker. While the water is heating, I weighed my yarn, which ended up being 9.18 grams. Then i measured out .918 grams of potassium aluminum sulfate (10% of the weight of the yarn) and .459 grams of cream of tartar (5% of the weight of the yarn). Once the water heated to just under boiling, about 90 degrees, I added the potassium aluminum sulfate and the tartaric acid to the beaker. Once the mixture was completely dissolved, i dampened the yarn by running it under some clean water and put the yarn in the beaker. Keeping the mixture at about 90 degrees consistently, I simmered the mixture for an hour, stirring occasionally to ensure that the yarn was fully submerged. After an hour of simmering, I removed the yarn and spread it out on a paper towel to dry completely before I dyed it.
In order to dye both the untreated yarn, which weighed 9.32 grams, and the Alum mordant-treated yarn, which weighed 9.18 grams, I used the same procedure for both, in separate batches: First I measured out exactly 1 oz. of dry, whole cochineal. I then used a mortar and pestle to grind the dry cochineal into a fine and uniform powder. Then I placed the cochineal powder into a 250 ml beaker and covered with 200 ml water, which I stirred to ensure that the powder was fully dissolved. I then let the cochineal mixture sit overnight to increase its depth of color. I repeated this process to make 2 identical dyes- 1 for the alum-mordant-treated yarn and 1 for the untreated yarn. The next day, I filled a 1000 ml beaker with 500 ml water and brought it to a boil. I then added the cochineal mixture and brought it back up to a boil, boiling for 15 minutes. During this 15 minutes, I made sure to skim off the froth and the impurities and solids that were rising to the top of the mixture, and discarded these. I then dampened the untreated yarn and added it to the mixture, mixing occasionally and simmering for 45 minutes at 95 degrees. I repeated this same procedure for the alum-mordant-treated yarn. After 45 minutes, I removed both the yarn skeins and spread them on paper towels to dry. After letting them dry for about an hour, I washed them in a cold-water bath to seal the color in, and spread them out again to dry fully.
Results
The results of my experiment surprised me in a couple different ways. Firstly, I was surprised by the dramatic difference in the colors produced by the same dye when one yarn was treated and one yarn wasn't: The alum-treated yarn created a much deeper scarlet color, while the untreated yarn produced a much more pink-purple color. Secondly, I was also surprised by how well the dye held to it's substrate: After washing both the yarns in cold-water baths, the colors have not leaked into the water at all, becoming more and more intact the more they were able to dry. Overall, I was satisfied with the results in both the quality of the dye and the noticeable difference in the colors the two treatments produced.
Conclusions
When using a homemade dye, a difference in color and depth of color can be produced by treating the yarn beforehand, in this case with an alum mordant.
In my experiment, the results were good but could have been improved in several ways. First, I think that straining the cochineal mixture after letting it sit overnight would have eliminated the need to skim off solids from the dye-bath when it was boiling and would have produced a cleaner experiment. There are also several other treatments that you can use to create different colors and depths of color, including after-treatments which are applied after the dyeing itself, which would have been interesting to experiment with. A lot of my experiment was done at home, which made some of the measurements more difficult to obtain, and so the accuracy of the liquid measurements I also feel could have been improved by doing the entire experiment in the lab.
References
[1] Dye. Wikimedia Foundation Inc., 29 Mar. 2010. Web. 6 May 2010. <http://en.wikipedia.org/wiki/Dye>.
[2] Garfield, Simon. Mauve: how one man invented a color that changed the world. New
York, New York: W. W. Norton & company Inc., 2000. Print.
[3] Christie, R M, Colour Chemistry, 2001, Royal Society of Chemistry, Cambridge.
[4,5] Price, Heulwen. "The Chemistry of Dyes." Undergraduate Web Projects 2002. University of Bristol, 20 June 2002. Web. 6 May 2010. <http://www.chm.bris.ac.uk/webprojects2002/price/first%20page.htm>.